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Human nature, mating motives may lead to murder, book theorizes

Killing is fundamentally in our nature, having evolved over thousands of years from intense competition for reproductive success, according to a new theory by Dr. David Buss, an evolutionary psychologist at The University of Texas at Austin.

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AUSTIN, Texas—Killing is fundamentally in our nature, having evolved over thousands of years from intense competition for reproductive success, according to a new theory by Dr. David Buss, an evolutionary psychologist at The University of Texas at Austin.

This theory explains the many striking patterns revealed in murder statistics, such as why men kill so much more often than women—87 percent of killers are men—and why the number of women murdered by their lovers is staggeringly high.

“Our minds have developed adaptations to kill, which is contrary to previous theories that murder is something outside of human nature—a pathology imposed from the distorting influences of culture, media images, poverty or child abuse,” Buss said.

Buss conducted an unprecedented set of studies while investigating the underlying motives and circumstances of murders which are featured in his new book “The Murderer Next Door: Why the Mind is Designed to Kill.” The book was released May 23.

Buss’s research showed that nearly all people express a willingness to kill in some circumstances—to prevent being killed or to defend their children from killers. Interestingly, men indicated an increased willingness to kill when their status or reputation was threatened which are important qualities in attracting a mate. They also expressed a willingness to kill when their mating prospects become dire; women did not.

In Buss’s sample of 429,729 homicide FBI files, 13,670 were cases in which a husband killed his wife. A husband discovering his wife having an extramarital affair is one of the leading causes of women being murdered, particularly when the woman is dramatically younger than her husband. This supports earlier research conducted by Buss of more than 10,000 people in 37 cultures that found that the traits men most valued in a mate were beauty, youth and fidelity. Unlike women whose internal fertilization guarantees she is the mother of her children, regardless of her partner’s sexual infidelities, before the days of paternity testing, a man had to rely solely on the fidelity of his mate. The homicide study leads to a disturbing theory—the more good-looking, healthy and fertile the woman, the more motivated the man will be to kill her upon discovering a sexual infidelity.

If a man’s partner leaves him for a rival male he loses access entirely to her future reproductive value. He also loses whatever maternal efforts she would have invested in his future children.

According to a study of homicides in Chicago, 50 percent of wife killings took place within the first two months of the separation, and an astonishing 85 percent of these women were killed within the first year.

“It is likely that the key danger is not the length of time per se but, rather, when the man realizes she will never return to him,” Buss said.

Among women killed by a partner they have separated from, 88 percent had been stalked prior to being killed. Although most stalkers do not kill their victims, most mate-killing men do stalk their victims.             

Men are at particularly high risk of being murdered when they poach someone’s committed mate from a relationship or when they humiliate another man in public. Police records show that a high percentage of male-on-male killings result from “trivial” altercations, which are hardly trivial in the minds of men. High numbers of male murders also are triggered by one man beating another in competition at work or in love.

As part of his research, Buss led the largest homicidal fantasy study ever conducted, using 5,000 people, 375 who were actual murderers. The study looked into why people have homicidal fantasies and the specific circumstances in which they contemplate killing. According to the study, the key differences between the sexes is not so much in having homicidal fantasies, but rather what triggers them. Among men who entertained thoughts of murdering their mates, 54 percent were triggered by women ending their relationships. Repeated physical, sexual and psychological abuse were the most common triggers of women’s homicidal fantasies, and also the leading predictors of when women kill their mates.             

Homicidal adaptations are so ingrained that 91 percent of men and 84 percent of women have had at least one fantasy of committing murder—often intense and astonishingly detailed. These fantasies were similar to those reported by actual murderers, and interviews with killers revealed that 72 percent of them reported such fantasies leading up to committing murder.

“When we asked people to estimate the probability that they would carry out their homicidal fantasies if they could get away with them undiscovered, men’s likelihood quadrupled,” Buss said. “The most frequently cited reason for not carrying through on homicidal fantasies was the fear of getting caught and spending their life behind bars.

“The evolutionary theory of murder helps us to understand when we are most at danger of being killed,” he added. “It reveals why mating motives lie behind most murders.  And it brings to light when our own homicidal circuits become activated and we, too, risk becoming victims or perpetrators.”

For more information contact: Michelle Bryant, College of Liberal Arts, 512-232-4730.